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    Response Processors: Request Captcha Processor: Incident - Bad Captcha Answer

    Complexity: Suspicious (1.0)

    Default Response: 10x = Captcha Answer Automation Incident.

    Cause: A captcha is a special technique used to differentiate between human users, and automated scripts. This is done through a Turing test, where the user is required to visually identify characters in a jumbled image and transcribe them into an input. If the user is unable to complete the challenge in a reasonable amount of time, they are not allowed to proceed with their original request. Because it is nearly impossible to script the deciphering of the image, automated scripts generally get stuck and cannot proceed. Additionally, an audio version is optionally available to allow users who have a visual handicap to complete the captcha successfully. Captchas are used in two different ways by the system. They can be explicitly added to any workflow within the protected web application (such as requiring a captcha to login, or checkout a shopping cart), and they can be used to test a suspicious user before allowing them to continue using the site (similar to blocking the user, but with a way for the user to unblock themselves if they can prove they are not an automated script). Captchas are generally used to resolve "Insufficient Anti-Automation" weaknesses in the protected web application. Regardless of which type of captcha is being used, this incident is generated when the user provides a bad solution to the captcha image. For example, the image may have said "Hello", but the user typed "hfii0" instead. Because the images can be somewhat difficult to read at times (in order to ensure a script cannot break them), it is not uncommon for a legitimate user to enter the wrong value a few times before getting it right, especially if they are unfamiliar with this type of technique.

    Behavior: Simply providing a bad solution to the captcha image is not necessarily malicious. Legitimate users are not always able to solve the captcha on the first try. However if a large volume of invalid solutions are provided, then it is more likely that a script is attempting to crack the captcha image through educated guessing and "Brute Force".

    Published: 2013-11-20